Field of the Invention
The invention relates to an energy storage battery, such as a redox flow battery.
Description of the Related Art
At present, energy storage is mainly performed using pumped-storage power generation. However, since construction of a pumped-storage power station involves limitations on site conditions, new energy storage techniques, particularly secondary batteries being highly technically and economically feasible, have been actively studied. In recent years, redox flow batteries have received attention as secondary batteries.
Conventionally, there have been proposed various electrolytes for use in a redox flow battery. For example, Patent Document 1 proposes a configuration in which the anode electrolyte is an aqueous solution containing an iron-based redox material as an anode active material, and also containing a chelating agent or complexing agent for shifting a potential to the negative side. Also, in recent years, for example, there is proposed a configuration in which the cathode electrolyte is an aqueous solution containing a manganese-based redox material as a cathode active material.
However, manganese oxides are known to have strong oxidizing power to decompose (oxidize) a wide range of organic substances in water. Hence, potassium permanganate, a kind of manganese oxide, is used as an oxidant to measure the amount of organic substances in water, i.e., COD value (Non-Patent Document 1). In addition, manganese ion also has strong oxidizing power. For example, it is known that even in a state that manganese ion is complexed with a chelating agent or complexing agent to form a complex such as Mn(III)-EDTA (ethylene diamine tetraacetic acid), the ligand may be oxidized to generate CO2 gas and thus cause self-decomposition of the complex (Non-Patent Document 2).
Accordingly, Patent Document 2 proposes using a chelating agent or complexing agent to prevent precipitation of a manganese compound. In addition, Patent Document 3 proposes using a chelating agent or complexing agent to improve reactivity of manganese ion in a cathode electrolyte of a microbial battery.